Network Working Group H. Soliman, Ed.
Internet-Draft Elevate Technologies
Intended status: Standards Track February 27, 2009
Expires: August 31, 2009
Mobile IPv6 Support for Dual Stack Hosts and Routersdraft-ietf-mext-nemo-v4traversal-09.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 31, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Soliman Expires August 31, 2009 [Page 1]

Internet-Draft dsmipv6 February 20092. Introduction
Mobile IPv6 [RFC3775] and [RFC3963] allow mobile nodes to move within
the Internet while maintaining reachability and ongoing sessions,
using an IPv6 home address or prefix. However, since IPv6 is not
widely deployed, it is unlikely that mobile nodes will initially use
IPv6 addresses only for their connections. It is reasonable to
assume that mobile nodes will, for a long time, need an IPv4 home
address that can be used by upper layers. It is also reasonable to
assume that mobile nodes will move to networks that might not support
IPv6 and would therefore need the capability to support an IPv4
Care-of Address. Hence, this specification extends Mobile IPv6
capabilities to allow dual stack mobile nodes to request that their
home agent (also dual stacked) tunnel IPv4/IPv6 packets addressed to
their home addresses, as well as IPv4/IPv6 care-of address(es).
Using this specification, mobile nodes would only need Mobile IPv6
and [RFC3963] to manage mobility while moving within the Internet;
hence eliminating the need to run two mobility management protocols
simultaneously. This specification provides the extensions needed in
order to allow IPv6 mobility only to be used by dual stack mobile
nodes.
This specification will also consider cases where a mobile node moves
into a private IPv4 network and gets configured with a private IPv4
Care-of Address. In these scenarios, the mobile node needs to be
able to traverse the IPv4 NAT in order to communicate with the home
agent. IPv4 NAT traversal for Mobile IPv6 is presented in this
specification.
In this specification, the term mobile node refers to both a mobile
host and mobile router unless the discussion is specific to either
hosts or routers. Similarly, we use the term home address to reflect
an address/prefix format. Note that both mobile host and router
functionality has already been defined in [RFC3775] and [RFC3963],
respectively. This specification does not change that already
defined behavior, nor does it extend the specific type of hosts and
router support already defined, except for two things: (i) allowing
the mobile node to communicate with its home agent even over IPv4
networks, and (ii) allowing the use of IPv4 home addresses and
prefixes.
In this specification, extensions are defined for the binding update
and binding acknowledgement. It should be noted that all these
extensions apply to cases where the mobile node communicates with a
Mobility Anchor Point (MAP) as defined in [RFC5380]. The
requirements on the MAP are identical to those stated for the home
agent, although it is unlikely that NAT traversal would be needed
Soliman Expires August 31, 2009 [Page 5]

Internet-Draft dsmipv6 February 2009
with a MAP as it is expected to be in the same address domain.
2.1. Motivation for Using Mobile IPv6 Only
IPv6 offers a number of improvements over today's IPv4, primarily due
to its large address space. Mobile IPv6 offers a number of
improvements over Mobile IPv4 [RFC3344], mainly due to capabilities
inherited from IPv6. For instance, route optimization and dynamic
home agent discovery can only be achieved with Mobile IPv6.
One of the advantages of the large address space provided by IPv6 is
that it allows mobile nodes to obtain a globally unique care-of
address wherever they are. Hence, there is no need for Network
Address Translator (NAT) traversal techniques designed for Mobile
IPv4. This allows Mobile IPv6 to be a significantly simpler and more
bandwidth efficient mobility management protocol. At the same time,
during the transition towards IPv6, NAT traversal for existing
private IPv4 networks needs to be considered. This specification
introduces NAT traversal for this purpose.
The above benefits make the case for using Mobile IPv6-only for dual
stack mobile nodes as it allows for a long lasting mobility solution.
The use of Mobile IPv6 for dual stack mobility eliminates the need
for changing the mobility solution due to the introduction of IPv6
within a deployed network.
2.2. Scenarios Considered by This Specification
There are several scenarios that illustrate potential
incompatibilities for mobile nodes using Mobile IPv6. Some of the
problems associated with mobility and transition issues were
presented in [RFC4977]. This specification considers the scenarios
that address all the problems discussed in [RFC4977]. The scenarios
considered in this specification are listed below.
All of the following scenarios assume that both the mobile node and
the home agent are IPv4 and IPv6-enabled and that only Mobile IPv6 is
used between the mobile node and the home agent. We also assume that
the home agent is always reachable through a globally unique IPv4
address. Finally, it's important to note that the following
scenarios are not mutually exclusive.
Scenario 1: IPv4-only foreign network
In this scenario, a mobile node is connected to an IPv4-only foreign
network. The mobile node can only configure an IPv4 Care-of Address.
Scenario 2: Mobile node behind a NAT
Soliman Expires August 31, 2009 [Page 6]

Internet-Draft dsmipv6 February 2009
In this scenario, the mobile node is in a private IPv4 foreign
network that has a NAT device connecting it to the Internet. If the
home agent is located outside the NAT device, the mobile node will
need a NAT traversal mechanism to communicate with the home agent.
Scenario 3: Home Agent behind a NAT
In this scenario, the communication between the mobile node and the
home agent is further complicated by the fact that the home agent is
located within a private IPv4 network. However, in this scenario, we
assume that the home agent is allocated a globally unique IPv4
address. The address might not be physically configured on the home
agent interface. Instead, it is associated with the home agent on
the NAPT device, which allows the home agent to be reachable through
address or port mapping.
Scenario 4: Use Of IPv4-only applications
In this scenario, the mobile node may be located in an IPv4, IPv6 or
a dual network. However, the mobile node might be communicating with
an IPv4-only node. In this case, the mobile node would need a stable
IPv4 address for its application. The alternative to using an IPv4
address is the use of protocol translators; however, end-to-end
communication with IPv4 is preferred to the use of protocol
translators.
The mobile node may also be communicating with an IPv4-only
application that requires an IPv4 address.
The cases above illustrate the need for the allocation of a stable
IPv4 home address to the mobile node. This is done using an IPv4
home address. Since running Mobile IPv4 and Mobile IPv6
simultaneously is problematic (as illustrated in [RFC4977]), this
scenario adds a requirement on Mobile IPv6 to support IPv4 home
addresses.
Scenario 5: IPv6 and IPv4-enabled networks
In this scenario, the mobile node should prefer the use of an IPv6
care-of address for either its IPv6 or IPv4 home address. Nomral IP
in IP tunnelling should be used in this scenario as described in
[RFC3775]. Under rare exceptions, where IP in IP tunnelling for IPv6
does not allow the mobile node to reach the home agent, the mobile
node follows the sending algorithm described in Section 5.4.1. UDP
tunnelling in IPv6 networks is proposed in this document as a last
resort mechanism when reachability cannot be achieved through normal
IP in IP tunnelling. It should not be viewed as a normal mode of
operation and should not be used as a first resort.
Soliman Expires August 31, 2009 [Page 7]

Internet-Draft dsmipv6 February 20093. Solution Overview
In order to allow Mobile IPv6 to be used by dual stack mobile nodes,
the following needs to be done:
o Mobile nodes should be able to use an IPv4 and IPv6 home or
care-of address simultaneously and update their home agents
accordingly.
o Mobile nodes need to be able to know the IPv4 address of the home
agent as well as its IPv6 address. There is no need for IPv4
prefix discovery however.
o Mobile nodes need to be able to detect the presence of a NAT
device and traverse it in order to communicate with the home
agent.
This section presents an overview of the extensions required in order
to allow mobile nodes to use Mobile IPv6 only for IP mobility
management
3.1. Home Agent Address Discovery
Dynamic home agent Address Discovery (DHAAD) was defined in [RFC3775]
to allow mobile nodes to discover their home agents by appending a
well-known anycast interface identifier to their home link's prefix.
However, this mechanism is based on IPv6-anycast routing. If a
mobile node is located in an IPv4-only foreign network, it cannot
rely on native IPv6 routing. In this scenario, the solution for
discovering the home agent's IPv4 address is through the Domain Name
System (DNS). If the MN is attached to an IPv6-only or dual stack
network, it may also use procedures defined in
[I-D.ietf-mip6-bootstrapping-integrated-dhc] to discover home agent
information. Note that the use of
[I-D.ietf-mip6-bootstrapping-integrated-dhc] cannot give the mobile
node information that allows it to communicate with the home agent if
the mobile node is located in an IPv4-only network. In this
scenario, the mobile node needs to discover the IPv4 address of its
home agent through the DNS.
For DNS lookup by name, the mobile node should be configured with the
name of the home agent. When the mobile node needs to discover a
home agent, it sends a DNS request with QNAME set to the configured
name. An example is "ha1.example.com". If a home agent has an IPv4
and IPv6 address, the corresponding DNS record should be configured
with both 'AAAA' and 'A' records. Accordingly, the DNS reply will
contain 'AAAA' and 'A' records.
Soliman Expires August 31, 2009 [Page 8]

Internet-Draft dsmipv6 February 2009
For DNS lookup by service, the SRV record defined in [RFC5026] is
reused. For instance, if the service name is "mip6" and the protocol
name is "ipv6" in the SRV record, the mobile node SHOULD send a DNS
request with the QNAME set to "_mip6._ipv6.example.com". The
response should contain the home agent's FQDN(s) and may include the
corresponding 'AAAA' and 'A' records as well.
If multiple home agents reside on the home link, each configured with
a public IPv4 address, then the operation above applies. The correct
DNS entries can be configured accordingly.
3.2. Mobile Prefix Solicitation and Advertisement
According to [RFC3775], the mobile node can send a Mobile Prefix
Solicitation and receive a Mobile Prefix Advertisement containing all
prefixes advertised on the home link.
A dual stack mobile node MAY send a Mobile Prefix Solicitation
message encapsulated in IPv4 (i.e., IPv6 in IPv4) in the case where
the mobile node has no access to IPv6 within the local network.
Securing these messages requires the mobile node to have a security
association with the home agent, using IPsec and based on the mobile
node's IPv4 care-of address as described in [RFC3775], and [RFC4877].
[RFC3775] requires the mobile node to include the home address option
in the solicitation message sent to the home agent. If the mobile
node is located in an IPv4 network, it will not be assigned an IPv6
address to include in the source address. In this case, the mobile
node MUST use its home address in the source address field of the
IPv6 packet, in addition to using the home address option as expected
by [RFC3775].
3.3. Binding Management
A dual stack mobile node will need to update its home agent with its
care-of address. If a mobile node has an IPv4 and an IPv6 home
address, it will need to create a binding cache entry for each
address. The format of the IP packet carrying the binding update and
acknowledgement messages will vary depending on whether the mobile
node has access to IPv6 in the visited network. There are three
different scenarios to consider with respect to the visited network:
o The visited network has IPv6 connectivity and provides the mobile
node with a care-of address (in a stateful or stateless manner).
o The mobile node can only configure a globally unique IPv4 address
in the visited network.
Soliman Expires August 31, 2009 [Page 9]

Internet-Draft dsmipv6 February 2009
o The mobile node can only configure a private IPv4 address in the
visited network.
3.3.1. Foreign Network Supports IPv6
In this case, the mobile node is able to configure a globally unique
IPv6 address. The mobile node will send a binding update to the IPv6
address of its home agent, as defined in [RFC3775]. The binding
update MAY include the IPv4 home address option introduced in this
document. After receiving the binding update, the home agent creates
two binding cache entries, one for the mobile node's IPv4 home
address, and another for the mobile node's IPv6 home address. Both
entries will point to the mobile node's IPv6 care-of address. Hence,
whenever a packet is addressed to the mobile node's IPv4 or IPv6 home
addresses, the home agent will tunnel it in IPv6 to the mobile node's
IPv6 care-of address included in the binding update. Effectively,
the mobile node establishes two different tunnels, one for its IPv4
traffic (IPv4 in IPv6) and one for its IPv6 traffic (IPv6 in IPv6)
with a single binding update.
In this scenario, this document extends [RFC3775] by including the
IPv4 home address option in the binding update message. Furthermore,
if the network supports both IP v4 and IPv6, or if the mobile node is
experiencing problems with IP in IP tunnelling, this document
proposes some mitigating actions as described in Section 5.4.1
After accepting the binding update and creating the corresponding
binding cache entries, the home agent MUST send a binding
acknowledgement to the mobile node as defined in [RFC3775]. In
addition, if the binding update included an IPv4 home address option,
the binding acknowledgement MUST include the IPv4 address
acknowledgment option as described later in this specification. This
option informs the mobile node whether the binding was accepted for
the IPv4 home address. If this option is not included in the binding
acknowledgement and the IPv4 home address option was included in the
binding update, the mobile node MUST assume that the home agent does
not support the IPv4 home address option and therefore SHOULD NOT
include the option in future binding updates to that home agent
address.
When a mobile node acquires both IPv4 and IPv6 care-of addresses at
the foreign network, it SHOULD prioritize the IPv6 care-of address
for its MIPv6 binding as described in Section 5.4.1.
3.3.2. Foreign Network Supports IPv4 Only
If the mobile node is in a foreign network that only supports IPv4,
it needs to detect whether a NAT is in its communication path to the
Soliman Expires August 31, 2009 [Page 10]

Internet-Draft dsmipv6 February 2009
home agent. This is done while exchanging the binding update and
acknowledgement messages as shown later in this document. NAT
detection is needed for the purposes of the signaling presented in
this specification.
3.3.2.1. Foreign Network Supports IPv4 Only (Public Addresses)
In this scenario the mobile node will need to tunnel IPv6 packets
containing the binding update to the home agent's IPv4 address. The
mobile node uses the IPv4 address it gets from the foreign network as
a source address in the outer header. The binding update will
contain the mobile node's IPv6 home address. However, since the
care-of address in this scenario is the mobile node's IPv4 address,
the mobile node MUST include its IPv4 care-of address in the IPv6
packet. The IPv4 address is represented in the IPv4 Care-of address
option defined in this specification. If the mobile node had an IPv4
home address, it MUST also include the IPv4 home address option
described in this specification.
After accepting the binding update, the home agent MUST create a new
binding cache entry for the mobile node's IPv6 home address. If an
IPv4 home address option were included, the home agent MUST create
another entry for that address. All entries MUST point to the mobile
node's IPv4 care-of address. Hence, all packets addressed to the
mobile node's home address(es) (IPv4 or IPv6) will be encapsulated in
an IPv4 header that includes the home agent's IPv4 address in the
source address field and the mobile node's IPv4 care-of address in
the destination address field.
After accepting the binding updates and creating the corresponding
entries, the home agent MUST send a binding acknowledgement as
specified in [RFC3775]. In addition, if the binding update included
an IPv4 home address option, the binding acknowledgement MUST include
the IPv4 address acknowledgment option as described later in this
specification. The binding acknowledgement is encapsulated to the
IPv4 care-of address, which was included in the source address field
of the IPv4 header encapsulating the binding update.
3.3.2.2. Foreign Network Supports IPv4 Only (Private Addresses)
In this scenario the mobile node will need to tunnel IPv6 packets
containing the binding update to the home agent's IPv4 address. In
order to traverse the NAT device, IPv6 packets are tunneled using UDP
and IPv4. The UDP port allocated for the home agent is TBD_DSMIPv6.
The mobile node uses the IPv4 address it gets from the visited
network as a source address in the IPv4 header. The binding update
will contain the mobile node's IPv6 home address.
Soliman Expires August 31, 2009 [Page 11]

Internet-Draft dsmipv6 February 2009
After accepting the binding update, the home agent MUST create a new
binding cache entry for the mobile node's IPv6 home address. If an
IPv4 home address option were included, the home agent MUST create
another entry for that address. All entries MUST point to the mobile
node's IPv4 care-of address included in the source address of the
IPv4 header that encapsulated the binding update message. In
addition, the tunnel used MUST indicate UDP encapsulation for NAT
traversal. Hence, all packets addressed to the mobile node's home
address(es) (IPv4 or IPv6) will be encapsulated in UDP then
encapsulated in an IPv4 header that includes the home agent's IPv4
address in the source address field and the mobile node's IPv4 care-
of address in the destination address field. Note that the home
agent MUST store the source UDP port numbers contained in the packet
carrying the binding update in order to be able to forward packets to
the mobile node.
After accepting the binding updates and creating the corresponding
entries, the home agent MUST send a binding acknowledgement as
specified in [RFC3775]. In addition, if the binding update included
an IPv4 home address option, the binding acknowledgement MUST include
the IPv4 address acknowledgment option as described later in this
specification. The binding acknowledgement is encapsulated in UDP
then IPv4 with the home agent's IPv4 address in the source address
field and the mobile node's IPv4 care-of address in the destination
field. The IPv4 address in the destination field of the IPv4 packet
is the source address received in the IPv4 header containing the
binding update message. The inner IPv6 packet will contain the home
agent's IPv6 address as a source address and the mobile node's IPv6
home address in the destination address field.
The mobile node needs to maintain the NAT bindings for its current
IPv4 care-of address. This is done through sending the binding
update regularly to the home agent.
3.4. Route Optimization
Route optimization, as specified in [RFC3775] will operate in an
identical manner for dual stack mobile nodes when they are located in
a visited network that provides IPv6 addresses to the mobile node and
while communicating with an IPv6-enabled correspondent node.
However, when located in an IPv4-only network, or when using the IPv4
home address to communicate with an IPv4 correspondent node, route
optimization will not be possible due to the difficulty of performing
the return routability test. In this specification, UDP
encapsulation is only used between the mobile node and its home
agent. Therefore, mobile nodes will need to communicate through the
home agent.
Soliman Expires August 31, 2009 [Page 12]

Internet-Draft dsmipv6 February 2009
Route optimization will not be possible for IPv4 traffic. That is,
traffic addressed to the mobile node's IPv4 home address. This is
similar to using Mobile IPv4, therefore there is no reduction of
features resulting from using this specification.
3.5. Dynamic IPv4 Home Address Allocation
It is possible to allow for the mobile node's IPv4 home address to be
allocated dynamically. This is done by including 0.0.0.0 in the IPv4
home address option included in the binding update. The home agent
SHOULD allocate an IPv4 address to the mobile node and include it in
the IPv4 address acknowledgement option sent to the mobile node. In
this case, the lifetime of the binding is bound to the minimum of the
lifetimes of the IPv6 binding and the lease time of the IPv4 home
address.
Soliman Expires August 31, 2009 [Page 13]

Internet-Draft dsmipv6 February 20094. Extensions And Modifications To Mobile IPv6
This section highlights the protocol and implementation additions
required to support this specification.
4.1. Binding Update Extensions4.1.1. IPv4 Home Address Option
This option is included in the Mobility Header including the binding
update message sent from the mobile node to a home agent or Mobility
Anchor Point. The alignment requirement for this option is 4n.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Prefix-len |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 home address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPv4 Home Address Option
Type
TBD
Length
6
Prefix-len
The length of the prefix allocated to the mobile node. If only a
single address is allocated, this field MUST be set to 32. In the
first binding update requesting a prefix, the field contains the
prefix length requested. However, in the following binding
updates, this field must contain the length of the prefix
allocated. A value of zero is invalid and MUST be considered an
error.
P
A flag indicating, when set, that the mobile node requests a
mobile network prefix. This flag is only relevant for new
requests, and must be ignored for binding refreshes.
Soliman Expires August 31, 2009 [Page 14]

Internet-Draft dsmipv6 February 2009
Reserved
This field is reserved for future use. It MUST be set to zero by
the sender and ignored by the receiver.
IPv4 Home Address
The mobile node's IPv4 home address that should be defended by the
home agent. This field could contain any unicast IPv4 address
(public or private) that was assigned to the mobile node. The
value 0.0.0.0 is used to request an IPv4 home address from the
home agent. A mobile node may choose to use this option to
request a prefix by setting the address to the All Zeroes and
setting the P flag. The mobile node could then form an IPv4 home
address based on the allocated prefix. Alternatively, the mobile
node may use two different options, one for requesting an address
(Static or Dynamic) and another for requesting a prefix.
4.1.2. The IPv4 Care-of Address Option
This option is included in the Mobility Header including the binding
update message sent from the mobile node to a home agent or Mobility
Anchor Point. The alignment requirement for this option is 4n.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Care-of address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The IPv4 CoA Option
Type
TBD
Length
6
Reserved
This field is set to zero by the sender and ignored by the
receiver.
Soliman Expires August 31, 2009 [Page 15]

Internet-Draft dsmipv6 February 2009
IPv4 Care-of Address
This field contains the mobile node's IPv4 care- of address. The
IPv4 care-of address is used when the mobile node is located in an
IPv4-only network.
4.1.3. The Binding Update Message Extensions
This specification extends the Binding Update message with two new
flags. The flags are shown and described below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P|F| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Binding Update message
F
When set, this flag indicates a request for forcing UDP
encapsulation regardless of whether a NAT is present on the path
between the mobile node and the home agent. This flag may be set
by the mobile node if it is required to use UDP encapsulation
regardless of the presence of a NAT. This flag SHOULD NOT be set
when the mobile node is configured with an IPv6 care-of address;
with the exception for the scenario mentioned in Section 5.4.14.2. Binding Acknowledgement Extensions4.2.1. IPv4 Address Acknowledgement Option
This option is included in the Mobility Header including the binding
acknowledgement message sent from the home agent or Mobility Anchor
Point to the mobile node. This option indicates whether a binding
cache entry was created for the mobile node's IPv4 address.
Additionally, this option includes an IPv4 home address in the case
of Dynamic IPv4 home address configuration (i.e., if the unspecified
IPv4 address was included in the binding update). The alignment
requirement for this option is 4n.
Soliman Expires August 31, 2009 [Page 16]

Internet-Draft dsmipv6 February 2009
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Status |Pref-len |Res|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 home address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: IPv4 Address Acknowledgement Option
Type
TBD
Length
6
Status
Indicates success or failure for the IPv4 home address binding.
Values from 0 to 127 indicate success. Higher values indicate
failure.
Pref-len
The prefix length of the address allocated. This field is only
valid in case of success and MUST be set to zero and ignored in
case of failure. This field overrides what the mobile node
requested (if not equal to the requested length).
Res
This field is reserved for future use. It MUST be set to zero by
the sender and ignored by the receiver
IPv4 Home Address
The IPv4 home address that the home agent will use in the binding
cache entry. This could be a public or private address. This
field MUST contain the mobile node's IPv4 home address. If the
address were dynamically allocated the home agent will add the
address to inform the mobile node. Otherwise, if the address were
statically allocated to the mobile node, the home agent will copy
it from the binding update message.
The following values are allocated for the Status field:
Soliman Expires August 31, 2009 [Page 17]

Internet-Draft dsmipv6 February 2009
o 0 Success
o 128 Failure, reason unspecified
o 129 Administratively prohibited
o 130 Incorrect IPv4 home address
o 131 Invalid IPv4 address
o 132 Dynamic IPv4 home address assignment not available
o 133 Prefix allocation unauthorized
4.2.2. The NAT Detection Option
This option is sent from the home agent to the mobile node to
indicate whether a NAT was in the path. This option MAY also include
a suggested NAT binding refresh time for the mobile node. This might
be usefl for scenarios where the mobile node is known to be moving
within the home agent's administrative domain, and therefore the NAT
timeout is known (through configuration) to the home agent. Section3.5 of [RFC5405] discusses issues with NAT timeout in some detail.
The alignment requirement for this option is 4n. If a NAT is
detected, this option MUST be sent by the home agent.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |F| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The NAT Detection Option
Type
TBD
Length
6
F
Soliman Expires August 31, 2009 [Page 18]

Internet-Draft dsmipv6 February 2009
This flag indicates to the mobile node that UDP encapsulation is
required. When set, this flag indicates that the mobile node MUST
use UDP encapsulation even if a NAT is not located between the
mobile node and home agent. This flag SHOULD NOT be set when the
mobile node is assigned an IPv6 care-of address; with the
exception for accomodating the scenarios discussed in
Section 5.4.1.
Reserved
This field is reserved for future use. It MUST be set to zero by
the sender and ignored by the receiver.
Refresh Time
A suggested time (in seconds) for the mobile node to refresh the
NAT binding. If set to zero, it is ignored. If this field is set
to all 1s it means that keepalives are not needed, i.e., no NAT
was detected. The home agent MUST be configured with a default
value for the refresh time. The recommended value is outlined in
Section 7Soliman Expires August 31, 2009 [Page 19]

Internet-Draft dsmipv6 February 20095. Protocol operation
This section presents the protocol operation and processing for the
messages presented above. In addition, this section introduces the
NAT detection and traversal mechanism used by this specification.
5.1. Tunelling Formats
This specification allows the mobile node to use various tunnelling
formats depending on its location and the visited network's
capabilities. The mobile node can tunnel IPv6 in IPv4, IPv4 in IPv6
or use UDP encapsulation to tunnel IPv6 in IPv4. Naturally, this
specification also supports tunnelling IPv6 in IPv6.
This specification allows UDP-based tunnelling to be used between the
mobile node and its home agent or MAP. A UDP encapsulation format
means the following order of headers:
IPv4/v6
UDP
IP (v4 or v6)
Other headers
Note that the ue of UDP encapsulation for IPv6 care-of addresses
SHOULD NOT be done except in the circumstances highlighted in
Section 5.4.1.
When using this format the receiver would parse the version field
following the UDP header in order to determine whether the following
header is IPv4 or IPv6. The rest of the headers are processed
normally. The above order of headers does not take IPsec headers
into account as they may be placed in different parts of the packet.
The above format MUST be supported by all implementations of this
specification and MUST always be used to send the binding update
message.
UDP Tunnelling can also encapsulate an ESP header as shown below.
IPv4/v6
UDP
ESP
Soliman Expires August 31, 2009 [Page 20]

Internet-Draft dsmipv6 February 2009
IP (v4 or v6)
Other headers
The negotiation of the secure tunnel format described above is
discussed in Section 6.2. The receiver of a UDP tunnel detects
whether an ESP header is present or not based on the UDP port used.
5.1.1. tunnelling Impacts on Transport and MTU
Changing the tunnel format may occur due to movement of the mobile
node from one network to another. This can have impacts on the link
and path MTU, which may affect the amount of bandwidth available to
the applications. The mobile node may use PMTUD as specified in
[RFC4459].
To accommodate traffic that uses Explicit Congestion Notification
(ECN), it is RECOMMENDED that the ECN and DSCP information is copied
between the inner and outer header as defined in [RFC3168] and
[RFC2983]. It is RECOMMENDED that the full-functionality option
defined in section 9.1.1 of [RFC3168]is used to deal with ECN.
Note that some impementations may not be able to use ECN over the UDP
tunnel. This is due to the lack of access to ECN bits in the UDP API
on most platforms. However, this issue can be avoided if UDP
encapsulation is done in the kernel.
Note that when using UDP encapsulation, the TTL field must be
decremented in the same manner as when IP in IP encapsulation is
used.
5.2. NAT Detection
This section deals with NAT detection for the purpose of
encapsulating packets between the mobile node and the home agent when
the mobile node is present in a private IPv4 network. Mobile IPv6
uses IKEv2 to establish te IPsec security association between the
mobile node and the home agent. IKEv2 has its own NAT detection
mechanism. However, IKEv2's NAT detection is only used for the
purpose of setting up the IPsec SA for secure traffic. The
interactions between the two NAT traversal mechanisms are described
in Section 6
NAT detection is done when the initial binding update message is sent
from the mobile node to the home agent. When located in an IPv4-only
foreign link, the mobile node sends the binding update message
encapsulated in UDP and IPv4. The source address of the IPv6 packet
is the mobile node's IPv6 home address. The destination address is
Soliman Expires August 31, 2009 [Page 21]

Internet-Draft dsmipv6 February 2009
the IPv6 address of the home agent. The IPv4 header contains the
IPv4 care-of address in the source address field and the IPv4 address
of the home agent in the destination address field.
When the home agent receives the encapsulated binding update, it
compares the IPv4 address of the source address field in the IPv4
header with the IPv4 address included in the IPv4 care-of address
option. If the two addresses match, no NAT device was in the path.
Otherwise, a NAT was in the path and the NAT detection option is
included in the binding acknowledgement. The binding
acknowledgement, and all future packets, are then encapsulated in UDP
and IPv4. The source address in the IPv4 header is the IPv4 address
of the home agent. The destination address is the IPv4 address
received in the IPv4 header encapsulating the binding update (this
address will be different from the IPv4 care-of address when a NAT is
in the path). The source port in the packet is the home agent's
source port. The destination port is the source port received in the
binding update message. Note that the home agent stores the port
numbers and associates them with the mobile node's tunnel in order to
forward future packets.
Upon receiving the binding acknowledgement with the NAT detection
option, the mobile node sets the tunnel to the home agent to UDP
encapsulation. Hence, all future packets to the home agent are
tunneled in UDP and IPv4. For all tunneled IPv6 packets, the source
address in the IPv6 header is the mobile node's IPv6 home address and
the destination address is the correspondent node's IPv6 address.
All tunneled IPv4 packets will contain the mobile node's IPv4 home
address in the source address field of the inner IPv4 packet and the
correspondent node's IPv4 address in the destination address field.
The outer IPv4 header is the same whether the inner packet is IPv4 or
IPv6.
If no NAT device was detected in the path between the mobile node and
the home agent then IPv6 packets are tunneled in an IPv4 header,
unless the home agent forces UDP encapsulation using the F flag. The
content of the inner and outer headers are identical to the UDP
encapsulation case.
A mobile node MUST always tunnel binding updates in UDP when located
in an IPv4-only network. Essentially, this process allows for
perpetual NAT detection. Similarly, the home agent MUST encapsulate
binding acknowledgements in a UDP header whenever the binding update
is encapsulated in UDP.
In conclusion, the packet formats for the binding update and
acknowledgement messages are shown below:
Soliman Expires August 31, 2009 [Page 22]

Internet-Draft dsmipv6 February 2009
Binding update received by the home agent:
IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
UDP header
IPv6 header (src=V6HOA, dst=HAADDR)
ESP Header
Mobility header
BU [IPv4 HAO]
IPv4 CoA option
Where V4ADDR is either the IPv4 care-of address or the address
provided by the NAT device. V6HOA is the IPv6 home address of the
mobile node. The binding update MAY also contain the IPv4 home
address option IPv4 HAO.
Binding acknowledgement sent by the home agent:
IPv4 header (src= HA_V4ADDR, dst=V4ADDR)
UDP Header
IPv6 header (src=HAADDR, dst=V6HOA)
ESP Header
Mobility Header
BA ([IPv4 ACK], NAT DET)
Where V6HOA is IPv6 home address of the mobile node. The IPv4 ACK is
the IPv4 address acknowledgement option, which is only included if
the IPv4 home address option were present in the BU. The NAT DET is
the NAT detection option, which MUST be present in the binding
acknowledgement message if the binding update was encapsulated in
UDP.
5.3. NAT Keepalives
If a NAT is detected, the mobile node will need to refresh the NAT
bindings in order to be reachable from the home agent. NAT bindings
can be refreshed through sending and receiving traffic encapsulated
in UDP. However, if the mobile node is not active, it will need to
Soliman Expires August 31, 2009 [Page 23]

Internet-Draft dsmipv6 February 2009
periodically send a message to the home agent in order to refresh the
NAT binding. This can be done using the binding update message. The
binding update/acknowledgement pair will ensure that the NAT bindings
are refreshed in a reliable manner. There is no way for the mobile
node to know the exact time of the NAT binding. The default time
suggested in this specification is NATKATIMEOUT. If the home agent
suggests a different refresh period in the binding acknowledgement,
the mobile node SHOULD use the value suggested by the home agent.
If the refresh time in the NAT detection option in the binding
acknowledgement is set to all 1s, the mobile node need not send
messages to refresh the NAT binding. However, the mobile node may
still be required to encapsulate traffic in UDP. This scenario may
take place when a NAT is not detected, but the home agent still
requires the mobile node to use UDP encapsulation.
It should be noted that a mobile node that does not need to be
reachable (i.e., only cares about the session continuity aspect of
Mobile IP) it does not need to refresh the NAT binding. In this
case, the mobile node would only be able to initiate communication
with other nodes. However, this is likely to imply that the mobile
node will need to send a binding update before initiating
communication after a long idle period as it is likely to be assigned
a different port and IPv4 address by the NAT when it initiates
communication. Hence, an implementation may choose, for the sake of
simplicity, to always maintain the NAT bindings even when it does not
need reachability.
Note that keepalives are also needed by IKEv2 over UDP port 4500.
This is needed for IKE dead peer detection, which is not handled by
DSMIPv6 keepalives.
5.4. Mobile Node Operation
In addition to the operations specified in [RFC3775] and [RFC3963],
this specification requires mobile nodes to be able to support an
IPv4 home address. This specification also requires the mobile node
to choose an IPv4 or an IPv6 care-of address. We first discuss
care-of address selection, then continue with binding management and
transmission of normal traffic.
5.4.1. Selecting a Care-of address
When a mobile node is in a dual stacked visited network, it will have
a choice between an IPv4 and an IPv6 care-of address. The mobile
node SHOULD prefer the IPv6 care-of address and bind it to its home
address(es). If a mobile node attempted to bind the IPv6 care-of
address to its home address(es) and the binding update timed out, the
Soliman Expires August 31, 2009 [Page 24]

Internet-Draft dsmipv6 February 2009
mobile node SHOULD:
o Resend the binding update using the exponential back-off algorithm
described in [RFC3775].
o If after three attempts in total a binding acknowledgement was not
received, the mobile node SHOULD send a new binding update using
the IPv4 care-of address. The exponential backoff algorithm
described in [RFC3775] should be used for re-transmission of the
binding update if needed.
This procedure should be used to avoid scenarios where IPv6
connectivity may not be as reliable as IPv4. This may take place
during early deployments of IPv6, or simply due to temporary outages
affecting IPv6 routing.
It is RECOMMENDED that upon movement the mobile node does not change
the IP address family chosen for the previous binding update unless
the mobile node is aware that it has moved to a different
administrative domain where previous problems with IPv6 routing may
not be present. Repeating the above procedure upon every movement
can cause significant degradation of the mobile node's applications'
performace due to extended periods of packet losses after handover if
the routing outage is still in effect.
When using an IPv4 care-of address and IP in IP encapsulation, if the
mobile node implementation is made aware by upper layers of
persistent packet losses, it may attempt to resend the binding update
with the F flag set, requesting UDP encapsulation for all packets.
This may avoid packet losses due to situations where local
firewalling policies prevent the use of IP in IP encapsulation.
The effect of these address selection mechanism is to allow the
follwing preferences in the absence of NAT:
1. IPv6
2. IPv4 (using IP in IP or UDP encapsulation if a NAT is detected)
3. UDP encapsulation when IP in IP is not allowed by the local
domain.
5.4.2. Sending Binding Updates
When sending an IPv6 packet containing a binding update while
connected to an IPv4-only access network, mobile nodes MUST ensure
the following:
Soliman Expires August 31, 2009 [Page 25]

Internet-Draft dsmipv6 February 2009
o The IPv6 packet is encapsulated in UDP.
o The source address in the IPv4 header is the mobile node's IPv4
care-of address.
o The destination address in the IPv4 header is the home agent's
IPv4 address.
o The source address in the IPv6 header is the mobile node's IPv6
home address.
o The IPv4 home address option MAY be included in the mobility
header. This option contains the IPv4 home address. If the
mobile node did not have a static home address it MAY include the
unspecified IPv4 address, which acts as a request for a dynamic
IPv4 home address. Alternatively, one or more IPv4 home address
options may be included with requests for IPv4 prefixes (i.e.,
with the P flag set).
o If the mobile node wishes to use UDP encapsulation only, it should
set the F flag in the binding update message.
o The IPv6 packet MUST be authenticated as per [RFC3775], based on
the mobile node's IPv6 home address.
When sending a binding update from a visited network that supports
IPv6, the mobile node MUST follow the rules specified in [RFC3775].
In addition, if the mobile node has an IPv4 home address or needs
one, it MUST include the IPv4 home address option in the mobility
header. If the mobile node already has a static IPv4 home address,
this address MUST be included in the IPv4 home address option.
Otherwise, if the mobile node needs a dynamic IPv4 address, it MUST
include the IPv4 0.0.0.0 address in the IPv4 home address option.
In addition to the rules in [RFC3775], the mobile node should follow
the care-of address selection guidelines in Section 5.4.1.
When the mobile node receives a binding acknowledgement from the home
agent, it follows the rules in [RFC3775] and [RFC3963]. In addition,
the following actions MUST be made:
o If the status field indicated failure with error code 144, the
mobile node MAY resend the binding update without setting the F
flag.
o If the mobility header includes an IPv4 address acknowledgement
option indicating success, the mobile node should create two
entries in its binding update list, one for the IPv6 home address
Soliman Expires August 31, 2009 [Page 26]

Internet-Draft dsmipv6 February 2009
and another for the IPv4 home address.
o If the NAT detection option were present, the mobile node MUST
tunnel future packets in UDP and IPv4. This MUST be indicated in
the binding update list.
o If no IPv4 address acknowledgement option were present, and an
IPv4 home address option was present in the binding update, the
mobile node MUST only create one binding update list entry for its
IPv6 home address. The mobile node MAY include the IPv4 home
address option in future binding updates.
o If an IPv4 address acknowledgement option were present and it
indicates failure for the IPv4 home address binding, the mobile
node MUST NOT create an entry for that address in its binding
update list. The mobile node MAY include the IPv4 home address
option in future binding updates.
5.4.2.1. Removing Bindings
Mobile nodes will remove bindings from the home agent's binding cache
whenever they move to the home link, or simply when mobility support
is not needed.
De-registering the IPv6 home address is described in [RFC3775]. The
same mechanism applies in this specification. Mobile nodes may
remove the binding for the IPv4 home address only, by sending a
binding update that does not include the IPv4 home address option.
Upon receiving this binding update, the home agent will replace the
existing cache entries with the content of the new message. This
ensures that the IPv4 home address binding is removed, while
maintining an IPv6 binding.
Note that the mobile node cannot remove the IPv6 home address binding
while maintaining an IPv4 home address binding.
A binding update message with a lifetime of zero, will remove all
bindings for the mobile node.
5.4.3. Sending Packets from a Visited Network
When the mobile node is located in an IPv6-enabled network it sends
and receives IPv6 packets as described in [RFC3775]. In cases where
IP in IP encapsulation is not providing connectivity to the home
agent, the mobile node may choose to encapsulate in UDP as suggested
in Section 5.4.1. However, this encapsulation of IPv6 traffic should
be used as a last resort as described. IPv4 traffic is encapsulated
in IPv6 packets to the home agent.
Soliman Expires August 31, 2009 [Page 27]

Internet-Draft dsmipv6 February 2009
When the mobile node is located in an IPv4 only network, it will send
IPv6 packets to its home agent according to the following format:
IPv4 header (src=V4CoA, dst=HA_V4ADDR)
[UDP Header]
IPv6 header (src=V6HoA, dst=CN)
Upper Layer protocols
Here the UDP header is only used if a NAT has been detected between
the mobile node and the home agent, or if the home agent forced UDP
encapsulation. V4CoA is the IPv4 care-of address configured by the
mobile node in the visited network.
Similarly, IPv4 packets are sent according to the following format:
IPv4 header (src=V4CoA, dst=HA_V4ADDR)
[UDP Header]
IPv4 header (src=V4HoA, dst=V4CN)
Upper Layer protocols
Here the UDP header is only used if a NAT has been detected between
the mobile node and the home agent, or if the home agent forced UDP
encapsulation.
5.4.4. Movement Detection in IPv4-only Networks
[RFC3775] describes movement detection mostly based on IPv6-specific
triggers and Neighbor Discovery [RFC4861] information. These
triggers are not available in an IPv4-only network. Hence, a mobile
node located in an IPv4-only network SHOULD use [RFC4436] for
guidance on movement detection mechanisms in IPv4-only networks.
The mobile node detects that it's in an IPv4-only network when the
IPv6 movement detection algorithm fails to configure an IPv6 address.
5.5. Home agent operation
In addition to the home agent specification in [RFC3775] and
[RFC3963], the home agent needs to be able to process the IPv4 home
address option and generate the IPv4 address acknowledgement option.
Both options are included in the mobility header. Furthermore, the
home agent MUST be able to detect the presence of a NAT device and
Soliman Expires August 31, 2009 [Page 28]

Internet-Draft dsmipv6 February 2009
indicate that in the NAT detection option included in the binding
acknowledgement.
A home agent must also act as a proxy for address resolution in IPv4
for the registered IPv4 home addresses of mobile nodes it is serving.
Moreover, the administrative domain of the home agent is responsible
for advertising the routing information of registered IPv4 mobile
network prefixes of the mobile nodes.
In order to comply with this specification, the home agent MUST be
able to find the IPv4 home address of a mobile node when given the
IPv6 home address. That is, given an IPv6 home address, the home
agent MUST store the corresponding IPv4 home address if a static one
is present. If a dynamic address were requested by the mobile node,
the home agent MUST store that address (associated with the IPv6 home
address) after it's allocated to the mobile node.
When the home agent receives a binding update encapsulated in UDP and
containing the IPv4 home address option, it needs to follow all the
steps in [RFC3775] and [RFC3963]. In addition, the following checks
MUST be done:
o If the IPv4 care-of address in the IPv4 CoA option is not the same
as the IPv4 address in the source address in the IPv4 header then
a NAT was in the path. This information should be flagged for the
binding acknowledgement.
o If the F flag in the binding update were set, the home agent needs
to determine whether it accepts forcing UDP encapsulation. If it
does not, the binding acknowledgement is sent with error code 144.
UDP encapsulation SHOULD NOT be used when the mobile node is
located in an IPv6-enabled link, with the exception of the
scenarios outlined in Section 5.4.1.
o If the IPv4 home address option contains a valid unicast IPv4
address, the home agent MUST check that this address is allocated
to the mobile node that has the IPv6 home address included in the
home address option. The same MUST be done for an IPv4 prefix.
o If the IPv4 home address option contained the unspecified IPv4
address, the home agent SHOULD dynamically allocate an IPv4 home
address to the mobile node. If none is available, the home agent
MUST return error code 132 in the status field of the IPv4 address
acknowledgement option. If a prefix were requested, the home
agent SHOULD allocate a prefix with the requested length; if
prefix allocation (of any length) was not possible, the home agent
MUST indicate failure of the operation with the appropriate error
code.
Soliman Expires August 31, 2009 [Page 29]

Internet-Draft dsmipv6 February 2009
o If the binding update is accepted for the IPv4 home address, the
home agent creates a binding cache entry for the IPv4 home
address/prefix. The home agent MUST include an IPv4
acknowledgement option in the mobility header containing the
binding acknowledgement.
o If the binding update is accepted for both IPv4 and IPv6 home
addresses, the home agent creates separate binding cache entries,
one for each home address. The care-of address is the one
included in the binding update. If the care-of address is an IPv4
address, the home agent MUST setup a tunnel to the IPv4 care-of
address of the mobile node.
When sending a binding acknowledgement to the mobile node, the home
agent constructs the message according to [RFC3775] and [RFC3963].
Note that the routing header MUST always contain the IPv6 home
address as specified in [RFC3775].
If the care-of address of the mobile node were an IPv4 address, the
home agent includes the mobile node's IPv6 home address in the
destination address field in the IPv6 header. If a NAT were
detected, the home agent MUST then encapsulate the packet in UDP and
an IPv4 header. The source address is set to the home agent's IPv4
address and the destination address is set to the address received in
the source address of the IPv4 header encapsulating the binding
update.
After creating a binding cache entry for the mobile node's home
addresses, all packets sent to the mobile node's home addresses are
tunneled by the home agent to the mobile node's care-of address. If
a NAT were detected, packets are encapsulated in UDP and IPv4.
Otherwise, if the care-of address is an IPv4 address, and no NAT were
detected, packets are encapsulated in an IPv4 header unless UDP
encapsulation is forced by the home agent.
5.5.1. Sending Packets to the Mobile Node
The home agent follows the rules specified in [RFC3775] for sending
IPv6 packets to mobile nodes located in IPv6 networks. When sending
IPv4 packets to mobile nodes in an IPv6 network, the home agent must
encapsulate the IPv4 packets in IPv6.
When sending IPv6 packets to a mobile node located in an IPv4
network, the home agent must follow the format negotiated in the
binding update/acknowledgement exchange. In the absence of a
negotiated format, the default format that MUST be supported by all
implementations is:
Soliman Expires August 31, 2009 [Page 30]

Internet-Draft dsmipv6 February 2009
IPv4 header (src= HA_V4ADDR, dst= V4ADDR)
UDP Header
IPv6 header (src=CN, dst= V6HoA)
Upper layer protocols
Where the UDP header is only included if a NAT were detected between
the mobile node and the home agent, or if the home agent forced UDP
encapsulation. V4ADDR is the IPv4 address received in the source
address field of the IPv4 packet containing the binding update.
When sending IPv4 packets to a mobile node located in an IPv4
network, the home agent must follow the format negotiated in the
binding update/acknowledgement exchange. In the absence of a
negotiated format, the default format that MUST be supported by all
implementations is:
IPv4 header (src= HA_V4ADDR, dst= V4ADDR)
[UDP Header]
IPv4 header (src=V4CN, dst= V4HoA)
Upper layer protocols
Where the UDP header is only included if a NAT were detected between
the mobile node and home agent, or if the home agent forced UDP
encapsulation.
5.6. Correspondent Node Operation
This specification has no impact on IPv4 or IPv6 correspondent nodes.
Soliman Expires August 31, 2009 [Page 31]

Internet-Draft dsmipv6 February 20096. Security Considerations
This specification allows a mobile node to send one binding update
for its IPv6 and IPv4 home addresses. This is a slight deviation
from [RFC3775] which requires one binding update per home address.
However, like [RFC3775], the IPsec security association needed to
authenticate the binding update is still based on the mobile node's
IPv6 home address. Therefore, in order to authorize the mobile
node's IPv4 home address binding, the home agent MUST store the IPv4
address corresponding to the IPv6 address that is allocated to a
mobile node. Therefore, it is sufficient for the home agent to know
that the IPsec verification for the packet containing the binding
update was valid provided that it knows which IPv4 home address is
associated with which IPv6 home address. Hence, the security of the
IPv4 home address binding is the same as the IPv6 binding.
In effect, associating the mobile node's IPv4 home address with its
IPv6 home address moves the authorization of the binding update for
the IPv4 address to the Mobile IPv6 implementation, which infers it
from the fact that the mobile node has an IPv6 home address and the
right credentials for sending an authentic binding update for the
IPv6 address.
This specification requires the use of IKEv2 as the default mechanism
for dynamic keying.
In cases where this specification is used for NAT traversal, it is
important to note that it has the same vulnerabilities associated
with [RFC3519]. An attacker is able to hijack the mobile node's
session with the home agent if it can modify the contents of the
outer IPv4 header. The contents of the header are not authenticated
and there is no way for the home agent to verify their validity.
Hence, a man in the middle attack where a change in the contents of
the IPv4 header can cause a legitimate mobile node's traffic to be
diverted to an illegitimate receiver independently of the
authenticity of the binding update message.
In this specification, the binding update message MUST be protected
using ESP transport mode. When the mobile node is located in an
IPv4-only network, the binding update message is encapsulated in UDP
as described earlier. However, UDP SHOULD NOT be used to encapsulate
the binding update message when the mobile node is located in an
IPv6-enabled network. If protection of payload traffic is needed
when the mobile node is located in an IPv4-only network,
encapsulation is done using tunnel mode ESP over port 4500 as
described in [RFC3948]. During the IKE negotiation with the home
agent, if the mobile node and home agent support the use of port
4500, the mobile node MUST establish the security association over
Soliman Expires August 31, 2009 [Page 32]

Internet-Draft dsmipv6 February 2009
port 4500, regardless of the presence of a NAT. This is done to
avoid the switching between ports 500 and 4500 and the potential
traffic disruption resulting from this switch.
Handovers within private IPv4 networks or from IPv6 to IPv4 networks
will have impacts on the security association between the mobile node
and the home agent. The following section presents the expected
behaviour of the mobile node and home agent in those situations. The
details of the IKE negotiations and messages are illustrated in
Section 6.26.1. Handover Interactions for IPsec and IKE
After the mobile node detects movement it configures a new care-of
address. If the mobile node is in an IPv4-only network, it removes
binding update list entries for correspondent nodes since route
optimisation cannot be supported. This may cause inbound packet
losses as remote correspondent nodes are unaware of such movement.
To avoid confusion in the correspondent node, the mobile node SHOULD
deregister its binding with each correspondent node by sending a
deregistration binding update. The deregistration binding update
message is tunnelled to the home agent and onto the correspondent
node. This is done after the mobile node updates the home agent with
its new location as discussed below.
The mobile node sends the binding update message to the home agent.
If the mobile node is in an IPv6-enabled network, the binding update
SHOULD be sent without IPv4/UDP encapsulation, unless UDP
encapsulation is needed as described in Section 5.4.1. If the mobile
node is in an IPv4-only network, then after IPsec processing of the
BU message, it encapsulates the BU in UDP/IPv4 as discussed in
sections 5.2 and 5.4. In order to be able to send the binding update
while in an IPv4-only network, the mobile node needs to use the new
IPv4 care-of address in the outer header, which is different from the
care-of address used in the existing tunnel. This should be done
without permanently updating the tunnel within the mobile node's
implementation in order to allow the mobile node to receive packets
on the old care-of address until the binding acknowledgement is
received. The method used to achieve this effect is implementation
dependent and is outside the scope of this specification. This
implies that the IP forwarding function (which selects the interface
or tunnel through which a packet is sent) is not based solely on the
destination address: some IPv6 packets destined to the home agent are
sent via the existing tunnel, while BUs are sent using the new
care-of address. Since BUs are protected by IPsec, the forwarding
function cannot necessarily determine the correct treatment from the
packet headers. Thus, the DSMIPv6 implementation has to attach
additional information to BUs, and this information has to be
Soliman Expires August 31, 2009 [Page 33]

Internet-Draft dsmipv6 February 2009
preserved after IPsec processing and made available to the forwarding
function, or additional DSMIP processing added to the forwarding
function. Depending on the mobile node's implementation, meeting
this requirement may require changes to the IPsec implementation.
Upon receiving the binding update message encapsulated in UDP/IPv4,
the home agent processes it as follows. In order to allow the
DSMIPv6 implementation in the home agent to detect the presence of a
NAT on the path to the mobile node, it needs to compare the outer
IPv4 source address with the IPv4 address in the IPv4 care-of address
option. This implies that the information in the outer header will
be preserved after IPsec processing and made available to the DSMIPv6
implementation in the home agent. Depending on the home agent's
implementation, meeting this requirement may require changes to the
IPsec implementation.
The home agent updates its tunnel mode security association to
include the mobile node's care-of address as the remote tunnel header
address, and 4500 as the port number. The IPv4 address and port
number are likely to be wrong; the mobile node provides the correct
information in a separate exchange as described below. When the
mobile node is located in a private IPv4 network (which is detected
as described above), the new address and port number are allocated by
the NAT. The home agent will also enable or disable UDP
encapsulation for outgoing ESP packets for the purpose of NAT
traversal.
If the Key Management Mobility Capability (K) bit was set in the
binding update, and the home agent supports this feature, the home
agent updates its IKE security associations to include the mobile
node's care-of address as the peer address and 4500 as the port
number. The home agent may also need to change NAT traversal fields
in the IKE_SA to enable the dynamic update of the IP address and port
number based on the reception of authenticated IKE messages, or
authenticated packets using tunnel mode ESP. The dynamic updates are
described in section 2.23 of RFC 4306. As described above, when the
mobile node is located in a private IPv4 network, the address and
port number used for IPsec and IKE traffic is not yet known by the
home agent at this point.
The mobile node updates the IKE SA in one of two ways. If the K flag
was set in the binding acknowledgement message, the mobile node
SHOULD send an empty informational message, which results in the IKE
module in the home agent to dynamically update the SA information.
The IKE implementation in the home agent is REQUIRED to support this
feature. Alternatively, the IKE SA should be re-negotiated. Note
that updating the IKE SA MUST take place after the mobile node has
sent the binding update and received the acknowledgement from the
Soliman Expires August 31, 2009 [Page 34]

Internet-Draft dsmipv6 February 2009
home agent.
It is important to note that the mobile node's IPv4 care-of address
seen by the DSMIPv6 module in the home agent upon receiving the
binding update may differ from the IPv4 care-of address seen by the
IKE module and the care-of address used for forwarding IPsec tunnel
mode traffic. Hence, it is probable that different modules in the
home agent will have a different care-of address that should be used
for encapsulating traffic to the mobile node.
After successfully processing the binding update, the home agent
sends the binding acknowledgement to the mobile node's care-of
address as received in the outer header of the packet containing the
binding update. Note that if the BU was rejected, the BAck is sent
to the same address where the BU was received from. This may require
special treatment in IP forwarding and/or IPsec processing which
resembles sending of BUs in the mobile node (described above).
Upon receiving the binding acknowledgement, the mobile node updates
its local tunnel mode Security Association information to include the
tunnel header IP source address, which is the mobile node's address
and the tunnel header IP destination, which is the home agent's
address. The mobile node may also need to enable or disable UDP
encapsulation for outgoing ESP packets for the purpose of NAT
traversal and the sending of keep alives.
The mobile node MAY use [RFC4555] to update its IKE SA with the home
agent. Using MOBIKE requires negotiating this capability with the
home agent when establishing the SA. In this case, the mobile node
and the home agent MUST NOT update their IPsec SAs locally as this
step is performed by MOBIKE. Furthermore, the use of MOBIKE allows
the mobile node to update the SA independently of the binding update
exchange. Hence, there is no need for the mobile node to wait for a
binding acknowledgement before performing MOBIKE. The use of MOBIKE
is OPTIONAL in this specification.
6.2. IKE negotiation messages between the mobile node and Home Agent
This specification defines a number of possible data encapsulation
formats depending on the mobile node's connectivity to the visited
network. When connected to an IPv6-enabled network, the tunnelling
formats are clear. However, when connected to an IPv4-only network,
care should be taken when negotiating the IKE association and the
consequential tunnelling formats used for secure and insecure
traffic. This section illustrates the IKE message exchange between
the mobile node and home agent when the mobile node is located in an
IPv4-only network. Two different IKE negotiations are considered:
Soliman Expires August 31, 2009 [Page 35]

Internet-Draft dsmipv6 February 2009
IF local_address = home_agent_1 &
remote_address = home_address_1 &
proto = MH & local_mh_type = BAck & remote_mh_type = BU Then use
SA ESP transport mode
where home_address_1 is the mobile node's registered IPv6 home
address and home_agent_1 is the IP address of the home agent
The above should result in BU/BA messages with the following BU
received by the home agent.
IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
UDP header (sport=Z, dport=DSMIPv6)
IPv6 header (src=V6HOA, dst=HAADDR)
ESP Header in Transport Mode
Mobility header
BU [IPv4 HAO]
IPv4 CoA option
(+ other as needed)
At the home agent, following UDP de-capsulation, the binding update
is delivered to the IPsec module as shown below:
IPv6 header (src=V6HOA, dst=HAADDR)
ESP Header in Transport Mode
Mobility header
BU [IPv4 HAO]
IPv4 CoA option
(+other as needed)
In addition, V4ADDR and the sport (Z) need to be passed with the
packet to ensure correct processing.
Following IPsec processing, the binding update is delivered to the
Soliman Expires August 31, 2009 [Page 37]

Internet-Draft dsmipv6 February 2009
DSMIPv6 home agent module as follows:
IPv6 header (src=V6HOA, dst=HAADDR)
Mobility Header
BU [IPv4 HAO]
IPv4 CoA option
(+other as needed)
In addition, V4ADDR and the sport (Z) need to be passed with the
packet to ensure correct processing.
The binding acknowledgement sent by the home agent module to the
IPsec module is as follows:
IPv6 header (src=HAADDR, dst=V6HOA)
Mobility Header
BA ([IPv4 ACK], NAT DET)
(+ other as needed)
In addition, V4ADDR, the sport from the BU (Z), and an indication
that UDP encapsulation must be used, need to be passed with the
packet to ensure correct processing.
The binding acknowledgement sent by the home agent to the mobile node
is as follows:
IPv4 header (src= HA_V4ADDR, dst=V4ADDR)
UDP Header (sport=DSMIPv6, dport=Z)
IPv6 header (src=HAADDR, dst=V6HOA)
ESP Header in Transport Mode
Mobility Header
BA ([IPv4 ACK], NAT DET)
Soliman Expires August 31, 2009 [Page 38]

Internet-Draft dsmipv6 February 20096.2.2. IKEv2 Operation for Securing Data over IPv4
To secure data traffic when the mobile node is located in an IPv4-
only network, the mobile node MUST establish a child_SA for that
purpose. The procedure is as follows:
Mobile Node Home Agent
----------- ----------
IPv4(source_addr=V4ADDR, dest_addr=HAADDR)
UDP (4500,4500) < non-ESP Marker > HDR, SK
{[N], SA, Ni, [KEi], TSi, TSr} -->
<--IPv4(source_addr=HAADDR, dest_addr=V4ADDR)
UDP (4500,Y) < non-ESP Marker > HDR, SK
SA, Nr, [KEr], TSi, TSr}
If no NAT is detected, the encapsulation used will be:
IPv4 (source_addr=v4CoA, dest_addr=HAAddr)
ESP
IP (source_addr=HoA, set_addr=CNAddr)
Upper_layer_HDR
where IP=IPv4 or IPv6 and HoA=v4HoA or v6HoA
If a NAT were detected, the encapsulation used will be:
IPv4 (source_addr=v4Addr, dest_addr=HAAddr)
UDP (sport=Y, dport=4500)
ESP
IP (source_addr=HoA, set_addr=CNAddr)
Upper_layer_HDR
Where v4CoA may be the external IPv4 address of the NAT, IP is either
an IPv4 or IPv6 header and HoA is either the IPv4 or the IPv6 HoA.
The above format shows the packet as seen by the home agent.
The SPD, whether a NAT were detected or not, is set as follows. Note
that this rule is designed to match all data from the MN to nodes
other than the home agent. This is done so that this rule does not
Soliman Expires August 31, 2009 [Page 39]

Internet-Draft dsmipv6 February 2009
overlap with the earlier rule securing BU/BA signaling between the MN
and the HA.
Mobile Node SPD-S:
IF local_address = home_address &
remote_address != home_agent &
proto=any, then use SA ESP tunnel mode
Initiate using IDi = user_1 to address home_agent_1
home agent SPD-S:
IF local_address != home_agent &
remote_address = home_address &
proto=any, then use SA ESP tunnel mode
Where home_address is the MN's registered IPv6 or IPv4 home address
and home_agent is the IPv6 or the IPv4 address of the home agent.
Soliman Expires August 31, 2009 [Page 40]

Internet-Draft dsmipv6 February 20098. Acknowledgements
Thanks to the following members (in alphabetical order) of the MIP6
and NEMO Working Groups for their contributions, discussion, and
review: Jari Arkko, Sri Gundavelli, Wassim Haddad, Conny Larsson,
Acee Lindem, Ahmad Muhanna, Vidya Narayanan, Karen Nielsen and
Keiichi Shima. Thanks to Karen Nielsen, Pasi Eronen and Christian
Kaas-Petersen for raising the issue of IKEv2 interactions and
proposing the solution included in this document. Thanks to Pasi
Eronen for the many thorough reviews of this document.
Soliman Expires August 31, 2009 [Page 42]

Internet-Draft dsmipv6 February 20099. IANA Considerations
The specification requires the following allocations from IANA:
A UDP port is needed for the NAT traversal mechanism described in
section 4.1.
The IPv4 home address option described in section 3.1.1 requires
an option type. This option is included in the Mobility header
described in [RFC3775].
The IPv4 address acknowledgement option described in section 3.2.1
requires a new option type. This option is included in the
Mobility header described in [RFC3775].
The NAT detection option described in section 3.2.2 requires a new
option type. This option is included in the Mobility header
described in [RFC3775].
The IPv4 Care-of address option described in section 3.1.2
requires a new option type allocation [RFC3775].
The Status field in the IPv4 home address option should be allocated
by IANA under the new registry: "DSMIPv6 IPv4 home address option
status codes".
The status field values are allocated using the following procedure:
1. New Status field values are allocated through IETF review. This
is for all RFC types including standards track, informational,
and experimental status that originate from the IETF and have
been approved by the IESG for publication.
2. Requests for new option type value assignments from outside the
IETF are only made through the publication of an IETF document,
per 1) above. Note also that documents published as "RFC Editor
contributions" [RFC4844] are not considered to be IETF documents.
Soliman Expires August 31, 2009 [Page 43]